Stabilization of halogenated hydrocarbons



United States PatentOfiice 2,721,883 Patented Oct. 25, 1955 STABILIZATION OF HALOGENATED HYDROCARBONS Henry C. Stevens, Akron, Ohio, assignor to Columbia- Southern Chemical Corporation, Allegheny County, Pa., a corporation of Delaware No Drawing. Application February 25, 1953, Serial No. 338,915

7 Claims. (Cl. 260652.5)

This invention relates to the stabilization of halogenated aliphatic hydrocarbons and it particularly concerns the stabilization of chlorinated aliphatic hydrocarbons. It further relates to stabilized compositions containing halogenated aliphatic hydrocarbons, notably chlorinated aliphatic hydrocarbons such as perchloroethylene.

It is known that chlorinated hydrocarbons such as perchloroethylene have a tendency to decompose during use, storage, and shipment. This tendency is known to be more pronounced when the chlorinated hydrocarbon is in contact with metallic surfaces such as iron or copper. Such decomposition renders these compounds objectionable when theyare employed for certain commercial operations.

One of the important commercial uses of perchloroethylene is as a solvent, for example, in dry cleaning of wearing apparel, rugs, or other fabric materials. It is an excellent solvent for oils and greases. However, when it decomposes, the products of decomposition interfere to such an extent as to materially injure its beneficial effect. When employed in metal structures, the problem of metal corrosion caused by the decomposition of the perchloroethylene is quite serious.

Moreover, these chlorinated hydrocarbons, and notably perchloroethylene have shown poor light stability. That is, under the effect of light, notably ultraviolet light or light of equivalent wave length, such as light from a fluorescent light, a change in the pH of the compound is observed. This change in the compound is often undesirable.

Various chemicals have heretofore been proposed for use as stabilizers for halogenated aliphatic hydrocarbons. Among those which have been suggested are benzaldehyde, cyclohexane, toluene, benzyl chloride, amylene hexylresorcinol, butyl mercaptan, ethyl acetate, guanidine, pyridine, and others. For certain purposes, these compounds are unsatisfactory in that they are ineffective stabilizers for perchloroethylene, or their odor or color is objectionable.

According to this invention, it has been discovered that chlorinated aliphatic hydrocarbons and notably perchloroethylene is satisfactorily stabilized when a small stabilizing quantity of N-methyl morpholine is added thereto. Such stabilized compositions have acceptable odor and color characteristics and exhibit enchanced light stability. Moreover, the stabilized compositions of this invention maintain their stability even though they have been distilled repeatedly.

The amount of N-methyl morpholine which is required to stabilize perchloroethylene, or like chlorinated aliphatic hydrocarbon, is exceedingly small. About 0.005 to 0.01 per cent of N-methyl morpholine, by weight of the composition, is desirable for optimum results. Somewhat smaller quantities of N-methyl morpholine in the perchloroethylene compositions also provide a stabilizing eifect. The concentration of N-methyl morpholine may be as high as about 1 to 2 per cent, or higher, if economically feasible. Perchloroethylene stabilized with N- methyl morpholine has been observed to remain stable over considerable periods of time even after repeated distillations.

The stabilizing efiect of N-methyl morpholine on perchloroethylene has been established, according to the invention, by means of a test conducted over a 72-hour period. The test is performed by refluxing perchloroethylene in a flask in the presence of water, strips of copper, and the stabilizer. One hundred milliliters of perchloroethylene is placed in a SOO-milliliter flask and 0.2 milliliter of water is added. The flask is attached to a small Soxhlet extractor and a bulb type Allihn condenser is attached to the extractor. One weighed copper strip is placed in each of the flask, extractor, and condenser. The copper strip which is placed in the condenser is placed so that the perchloroethylene condenses on the strip. The condenser is connected to a water scrubber to absorb any HCl evolved during the test. The perchloroethylene is heated to boiling point, the heating being carried out so that the extractor empties at 8 to 10-minute intervals. A -watt incandescent bulb is placed one inch from the vapor line of the extractor to furnish energy for photochemical oxidation.

After the test is completed, part of the water in the scrubber is poured through the condenser and extractor and finally into the flask. The water and perchloroethylene are poured into a beaker, phenolphthalein is added, and the water layer is titrated with 0.01 N NaOH. The copper strips are weighed to determine their weight loss during the test.

The light stability of perchloroethylene was determined by the following procedure. A fluorescent fixture with a 13 by 50-inch white reflector and two 40-watt, 47-inch cool-white bulbs spaced on 5-inch centers, such that there was a 3 /2-inch space between the bulbs, was mounted in a cradle upside down. One hundred-millimeter samples of the perchloroethylene composition to be tested for light stability were placed in 250-milliliter, glass-stoppered, squatty-type, clear glass bottles. These sample-containing bottles were placed between the bulbs in the 3%-inch space and exposed for 24 hours to the light from the two bulbs. No bottle was placed within 6 inches of either end of the bulb. The pH of the samples at the conclusion of the exposure was determined as was the pH prior to such exposure. A difference in pH of over 1 indicated poor light stability.

The following table presents the data observed when the above-described tests were made:

Acidity Millimeters of 0.01 N NaOH per 100 Milliliters of 02014 Copper Weight Losses PH (milligrams) Weight Percent N-Methyl Morpholine Extractor Photooxidation Flask denser 1 Below 2. pH of 2.

stabilizer for halogenated aliphatic hydrocarbons, or under certain circumstances, it may be utilized in conjunction with other stabilizers. Some stabilizers are reputed to be'satisfactory except insofar as their ability to provide suitable light stability. If, for some particular reason, one such stabilizer is desired, N-methyl morpholine may be employed therewith as an auxiliary sta bilizer to impart better light stability characteristics to the halogenated aliphatic hydrocarbon. When used as an auxiliary stabilizer, N-methyl morpholine in concentrations of from about 0.0025 per cent to 0.005 per cent by weight of the composition may be employed. Of course, higher concentrations comparable to those employed when N-methyl morpholine is the only stabilizer present may be used.

Although the present invention has been described with reference to specific details of certain embodiments, it is not intended that such details shall be regarded as limitations upon the scope of the invention, except insofar as included in the accompanying claims.

I claim:

1. The method of stabilizing halogenated aliphatic hydrocarbons containing up to 3 carbon atoms which comprises adding thereto a small stabilizing quantity of N-methyl morpholine.

2. The method of stabilizing chlorinated aliphatic hydrocarbons containing up to 3 carbon atoms which comprises adding thereto a small stabilizing quantity of N- methyl morpholine.

3. The method of stabilizing perchloroethylene which comprises adding thereto a small stabilizing amount of N-methyl morpholine.

4. A composition of matter comprising a halogenated aliphatic hydrocarbon containing up to 3 carbon atoms and a stabilizing amount of N-methyl morpholine.

5. A composition of matter comprising a chlorinated aliphatic hydrocarbon containing up to 3 carbon atoms and a stabilizing amount of N-methyl morpholine.

6. A composition of matter comprising perchloroethylene and a stabilizing amount of N-methyl morphol- 7. The composition of claim 6 wherein N-methyl morpholine is present in amount corresponding to at least 0.002 per cent by weight of the perchloroethylene and N-methyl morpholine.

References Cited in the file of this patent UNITED STATES PATENTS 

1. THE METHOD OF STABILIZING HALOGENATED ALIPHATIC HYDROCARBONS CONTAINING UP TO 3 CARBON ATOMS WHICH COMPRISES ADDING THERETO A SMALL STABILIZING QUANTITY OF N-METHYL MORPHOLINE. 